Add Micrometer support

[Meijuh]

This PR adds support for Micrometer and the contribution of is threefold.

1. Add names to Limits. These names are included as tags with name id in meters.
2. Implement MetricRegistry using Micrometer's MeterRegistry.
3. Add kind tags to both Limits and Limiters. This is useful in observability to distinguish between different Limits and Limiters. An example of this is shown in README.md under section Micrometer.

Note that 1. is a prerequisite for 2.; Micrometer will return existing meters for the same set of "meter name" + tags. Hence we need to distinguish different meters with different names + tags. I am not too familiar with Spectator; I believe there new meters are always created and hence, this may be a breaking change and should be properly evaluated (as each meter will now have an id tag).
Conceptually, a single Limit can be shared among several Limiters, therefore imo, it make sense to give each Limit its own name anyway.

[umairk79]

Hi @Meijuh, thanks for the contribution! I will take a look at this tomorrow.